Thin composite explosive products and preparation thereof

ABSTRACT

A composite explosive product, wherein its composition expressed as percentages by weight includes 85% to 92% of organic energetic charges; the organic energetic charges a) being selected from charges of octogen (HMX), hexogen (RDX), hexanitrohexaazaisowurtzitane (CL20), penthrite (PETN), and mixtures thereof, and b) presenting a grain size distribution with a value for D90 less than 15 μm and a value for D50 less than or equal to 5 μm; and 7% to 12% of a polymer gum selected from polyurethane-polyester gums, polyurethane-polyether gums, and mixtures thereof, of number average molecular weight greater than 20,000 g/mol and of Mooney viscosity lying in the range 20 to 70 ML (5+4) at 100° C.; and wherein the composite explosive product has a thickness lying in the range 0.4 mm to 5 mm.

The present invention relates to thin composite explosive products (of well-controlled small thickness) that are shapeable (i.e. deformable, by the action of temperature, with conservation of shape) and that are of high performance.

They contain a large content of energetic charges in a binder of specific nature. They consist in particular in sheets or in products obtained by cutting up such sheets, such as miniature arrays for multipoint initiation of explosive charges, e.g. explosive warheads.

The present invention also provides a method of preparing such composite explosive products. Said method is particularly easy to perform: at temperatures that are entirely compatible with the sensitivity of the energetic charges present, without using solvent, and including operations of only one type.

For explosives in the form of a sheet or a bar (generally of section that is circular, square, or rectangular), there exists a dimensional value, relating to sheet thickness or bar section, below which detonation initiated at a point attenuates and then ceases after traveling a certain distance, leaving a portion of the explosive intact. This minimum dimension (thickness or section) below which there is no stable propagation of detonation is referred to as the critical detonation thickness or section. For a cylindrical bar, mention is also made of a critical detonation diameter.

This critical detonation dimension is determined from samples of decreasing size (e.g. cylindrical stepped bars of decreasing section), with detonation being initiated at the end of the sample having the largest dimension (the end of the bar presenting the greatest section).

In certain applications, it is desired to have high performance explosives of small thickness. It is nevertheless clearly essential for the thickness to remain greater than the critical detonation dimension. It is therefore desirable to discover explosives of critical detonation dimension that is as small as possible. Such a small critical detonation dimension is advantageously less than or equal to 5 millimeters (mm), or indeed less than or equal to 1.5 mm, or even less than or equal to 1 mm. Thus, in the context of miniaturized arrays for multipoint initiation of explosive charges (where such an array may have the shape shown in FIG. 5 of patent application WO 2010/066752, for example), it is desired to have explosives with a critical detonation dimension that is as small as possible in order to make up the channels of said arrays (presenting a section that is as small as possible but nevertheless capable of propagating the detonation, including at corners).

In the prior art, there has thus already been interest in high performance explosives of small thickness and in obtaining them.

Patent U.S. Pat. No. 3,354,010 describes explosive products in the form of flexible sheets (typically having a thickness of 6.3 mm), of composition that contains organic energetic charges of the hexogen (HMX) and/or octogen (RDX) type in a binder (nitrocellulose) that is plasticized (tributyl acetylcitrate). Those products are obtained a priori by using two methods, both of which are relatively complex to perform: 1) obtaining a mixture comprising a solvent, evaporating said solvent, obtaining granules, and then shaping by extrusion, molding, or rolling; or 2) using hot mixing to obtain a paste comprising ethanol and rolling said paste.

Elastomers (gums, “uncured” rubbers (i.e. “green” rubbers)) of the polyurethane-polyester type (i.e. of polyurethane nature with flexible segments of polyester type) and/or of polyurethane-polyether type (i.e. of polyurethane nature with flexible segments of polyether type), have also been made commercially available for several years, in particular under the trademark Urepan® from the supplier RheinChemie, and under the trademark Millathane® by the supplier TSE Industries. The present invention provides an original opening for this type of elastomer.

In such a context, the person skilled in the art is always on the lookout for an explosive product that is of small (and well-controlled) thickness, that is shapeable, that presents high performance (i.e. a critical detonation dimension that is small (with reference to its small thickness (see above)), and that is easy to fabricate.

The inventors have the merit of proposing such a product that is constituted essentially by specific energetic charges (said “highly” energetic charges, i.e. “sensitive charges” being present in the form of fine grains (micrometer size) at a “maximum” content (≥85% by weight)) together with a binder of a novel type, said binder making it possible to obtain said product by a method that is particularly easy to perform (not requiring the use of a solvent, the viscosity of the binder not requiring high temperature (dangerous, given the sensitivity of the charges), requiring operations of only one type, in a single type of device (cylinder (roller) mill(s)), or indeed in a single device (cylinder (roller) mill) (see below)). It was not obvious to obtain explosive products having a high content of fine grain size charges, and even less obvious to obtain such products by a method that is easy to perform.

In a first aspect, the present invention thus provides novel composite explosive products. Said products, which present a critical detonation dimension that is small given their specific composition (composition containing a high content of charges, charges that are “highly” energetic, i.e. “sensitive”, and of fine grain size) thus combine a thickness that is small (although naturally greater than or equal to the critical detonation dimension) to said specific composition. In characteristic manner, the composite explosive products of the invention present:

-   -   a composition expressed as percentages by weight comprising:         -   +85% to 92%, advantageously 88% to 90% of organic energetic             charges; said organic energetic charges a) being selected             from charges of octogen (HMX), hexogen (RDX),             hexanitrohexaazaisowurtzitane (CL20), penthrite (PETN), and             mixtures thereof, and b) presenting a grain size             distribution with a value for D₉₀ less than 15 micrometers             (μm) and a value for D₅₀ less than or equal to 5 μm; and         -   +7% to 12%, advantageously 8% to 10% of a polymer gum             selected from polyurethane-polyester gums,             polyurethane-polyether gums, and mixtures thereof, of number             average molecular weight greater than 20,000 grams per mole             (g/mol) and of Mooney viscosity lying in the range 20 to 70             ML (5+4) at 100° C.; and     -   a thickness lying in the range 0.4 mm to 5 mm, advantageously in         the range 1 mm to 2 mm.

It can be seen immediately that the specified ranges for the contents of charges and of binder are narrow ranges. It is with such contents of charges (of specified nature and of specified (fine) grain size) and of binder (of specified nature) that the looked-for results have been obtained. Products that are obtained with a greater quantity of charges (assuming that it is indeed possible to “obtain” said products) present mechanical properties that are not satisfactory; products obtained with a smaller quantity of charges present energy performance (and in particular the critical detonation dimensions) that is not satisfactory (it should be recalled that it is desired to obtain critical detonation dimensions that are less than or equal to 5 mm, less than or equal to 1.5 mm, or even less than or equal to 1 mm).

As mentioned above, the composite explosive products of the invention thus include a large content of charges, organic charges that are “strongly” energetic (“sensitive”) and of fine grain size in a binder of a novel type.

The composite explosive products of the invention contain 85% to 92%, advantageously 88% to 90% (percentages by weight) of specific organic energetic charges.

The charges in question are charges that are “strongly” energetic (“sensitive”). They are octogen (HMX) charges, hexogen (RDX) charges, hexanitrohexaazaisowurtzitane (CL20) charges, penthrite (PEEN) charges, or a mixture of such charges. Advantageously, they are hexogen (RDX) charges, hexanitrohexaazaisowurtzitane (CL20) charges, or a mixture of these two types of charge (the most energetic).

The charges in question are not present in the form of large and small crystals, they are present in the form of small crystals only. They are charges (fines) that present a grain size distribution with a value for D₉₀ that is less than 15 μm and a value for D₅₀ that is less than or equal to 5 μm (thus specifying the notions of charges that are “fines” and crystals that are “small”). The value for D₁₀ is not specified insofar as it is not critical in any way. It can be understood that the finer the charges (i.e. the lower the value for D₁₀ (e.g. a value of 100 nanometers (nm) or even smaller)), the more advantageous the products in question. This grain size data (D₉₀, D₅₀ (and D₁₀)) is measured using photon correlation spectroscopy-diffusion light scattering (PCS-DLS) grain size measurement using a procedure defined in standard NF 11-666. They correspond respectively to the diameter at which the cumulative volume percentage (of particles of charge) is equal to 90%, 50% (median diameter) (and 10%).

Such fine charges are generally obtained by grinding “large” crystals. The person skilled in the art knows numerous grinding methods that are suitable for the sensitivity of the charges in question. In entirely non-limiting manner, mention may be made of the possibility of using Sweco® grinders. The Applicant has also described in French patent application FR 14/00669, published under the U.S. Pat. No. 3,018,807 (on Sep. 25, 2015), an original grinding method for obtaining CL20 charges having submicrometer monomodal grain size. That method comprises continuously grinding a charge of CL20 crystals of grain size greater than one micrometer (D₅₀>1 μm), in suspension in a liquid; said grinding being performed, with cooling, by multiple passes of the suspension through a horizontal axis flow attrition grinder with stirred grinding media.

The organic energetic charges (present in quantities, of nature, and of grain size, as specified above) are thus to be found in the composition of composite explosive products of the invention within a binder that is original.

Said binder is a polymer gum:

-   -   selected from polyurethane-polyester gums (i.e. of polyurethane         nature with flexible segments of polyester type),         polyurethane-polyether gums (i.e. of polyurethane nature with         flexible segments of polyether type), and mixtures thereof;     -   that presents a number average molecular weight that is greater         than 20,000 g/mol (advantageously greater than 35,000 g/mol,         most advantageously greater than 75,000 g/mol (particularly in         terms of the ability of the final product to withstanding         aging)); and     -   that presents Mooney viscosity lying in the range 20 to 70 ML         (5+4) at 100° C. This parameter is in widespread use in the         rubber industry. “x ML (5+4) at 100° C.” should be read “x M         equal to the viscosity in Mooney units (or points); L or S (L in         this example) corresponding to the size of the rotor, 5 giving         the preheating time of the product and 4 giving the time in         minutes after starting the motor at which the measurement is         read, 100° C. being the temperature of the measurement”. The         value “x” is generally specified to within “±y”; it is said         value “x” that needs to lie in the range 20 to 70 (extreme         values included).

Such a gum, with the specified proportions (7% to 12% (advantageously only 8% to 10%), it being recalled that the products in question have a large charge content) is entirely suitable for the purposes of the invention insofar as:

1) it enables the large content of fine charges to be incorporated and enables the mixture (charges+binder) to be worked mechanically at low temperature, i.e. at a temperature of less than 120° C., generally than less than 100° C. (advantageously in the range 60° C. to 80° C.) (which temperature is entirely compatible with the stability of the charges present), and this can be done without using solvent; and

2) it confers the required mechanical properties to the (thin) final product: mechanical strength, cohesion, shapeability. The products of the invention can be shaped insofar as said gum is shapeable. When raised to an appropriate temperature, it can be shaped and subsequently conserve the shape it has been given. This shape can be modified only by a further action of temperature.

The inventors have the merit of identifying (selecting) this type of binder, which is entirely suitable for the purposes of the invention. Other types of binder have been tested and have not given satisfactory results (as to the possibility of obtaining the mixture, of working at low temperature, and/or as to the properties of the final product of small thickness).

The binder of products of the invention generally consists in a polyurethane-polyester gum or a polyurethane-polyether gum, however it is possible to use mixtures of at least two gums (at least two polyurethane-polyester gums, at least two polyurethane-polyether gums, or at least one polyurethane-polyester gum and at least one polyurethane-polyether gum; such mixtures of gums (gums in the meaning of the invention) constituting a gum in the meaning of the invention) presenting the required properties (set out above)). Said binder advantageously consists in a polyurethane-polyester gum.

The composition of pyrotechnic composite products of the invention may further include at least one plasticizer selected from energetic plasticizers, non-energetic plasticizers, and mixtures thereof; it may further include generally up to 4% by weight of at least one such plasticizer. Such an at least one plasticizer (=at least one energetic plasticizer, at least one non-energetic plasticizer, or at least one energetic plasticizer and at least one non-energetic plasticizer) that is advantageously present (for obtaining the product and its properties) is generally present at a content of 1% to 4% by weight, advantageously 2% by 3% by weight.

Said at least one plasticizer is thus selected from non-energetic plasticizers (e.g. dioctyl azelate (DOZ), di-2-ethylhexyl sebacate (DOS), di-n-octyl phthalate (DOP), triacetin, and mixtures thereof), energetic plasticizers (advantageously of nitrate or nitramine type, e.g. diethylene glycol dinitrate (DEGDN), triethylene glycol dinitrate (TEGDN), butanetriol trinitrate (BTTN), trimethylolethane trinitrate (TMETN), a mixture of 2,4-dinitro-2,4-diaza-pentane, of 2,4-dinitro-2,4-diaza-hexane, and of 3,5-dinitro-3,5-diaza-heptane (and most particularly DNDA 5,7), nitrato ethyl nitramines (and in particular methyl-2-nitratomethyl nitramine (methylNENA) and ethyl-2-nitratoethyl nitramine (ethylNENA)), and mixtures thereof.

In a preferred variant, the composition of composite pyrotechnic products of the invention includes, as a plasticizer, triethylene glycol dinitrate (TEGDN).

The composition of composite pyrotechnic products of the invention is thus constituted essentially, or indeed entirely, of energetic charges, the binder, and optionally at least one plasticizer (that is advantageously present (see above)). It may be constituted to 100% by weight of said energetic charges, of said binder, and of said optional at least one plasticizer (charges+binder=100%, or charges+binder+plasticizer=100%). It is generally so constituted at at least 99% by weight. Specifically, it is not impossible that in addition to said charges, binder, and optional plasticizer(s), it also includes at least one additive. When present, such an at least one additive is generally present at a content lying in the range 0.1% to 1% by weight. In particular, it may comprise at least one working agent (candillila wax and/or paraffin, for example).

The advantageous variants in contents of charges, of binder, and of plasticizers specified above should be read independently or in combination.

In a variant, the composition of composite explosive products of the invention thus contains:

+88% to 90% of organic energetic charges; said organic energetic charges a) being selected from charges of octogen (HMX), hexogen (RDX), hexanitrohexaazaisowurtzitane (CL20), penthrite (PETN), and mixtures thereof, and b) presenting a grain size distribution with a value for D₉₀ less than 15 μm and a value for D₅₀ less than or equal to 5 μm; and

+8% to 10% of a polymer gum selected from polyurethane-polyester gums, polyurethane-polyether gums, and mixtures thereof, of number average molecular weight greater than 20,000 g/mol (advantageously greater than 35,000 g/mol, most advantageously greater than 75,000 g/mol) and of Mooney viscosity lying in the range 20 to 70 ML (5+4) at 100° C.;

+1% to 4%, advantageously 2% to 3% of a plasticizer, selected from energetic plasticizers, non-energetic plasticizers, and mixtures thereof; and

+0% to 1% of at least one additive.

In the context of this variant, said composition generally consists in the specified ingredients.

To their characteristic composition as specified above, the composite explosive products of the invention associate a small thickness. It has to be understood that a product of the invention presents a (single) thickness (e), a thickness (e) that is uniform and constant (well-controlled): 0.4 mm≤e≤5 mm, advantageously 1 mm≤e≤2 mm. Most advantageously, they present a thickness: e≤1.5 mm.

Obtaining products having a thickness of less than 0.4 mm is practically impossible, particularly since such products would need to be of very high performance (i.e. they would need to present a critical detonation dimension of less than 0.4 mm).

Obtaining products having a thickness greater than 5 mm is of little interest (the products in question presenting high performance at 5 mm, or indeed at smaller thickness) and, in any event, leads to problems with the shapeability of said products, and with controlling their thickness when it is greater than 5 mm.

In the light of the thickness values given above (0.4 mm≤e≤5 mm, advantageously 1 mm≤e≤2 mm, most advantageously, e≤1.5 mm), the person skilled in the art can understand the merits of the inventors in proposing such high performance composite explosive products (the explosive in question necessarily needing to present a critical detonation dimension that is less than those small values) which also have suitable mechanical properties (mechanical strength, cohesion, shapeability). The good results that have been obtained rely essentially on the binder (the nature of the binder) which, in association with an appropriate method (see below) makes it possible to incorporate a large content of (“sensitive”) charges of fine grain size within said binder.

The composite pyrotechnic products of the invention, as described above (presenting the above-specified composition and the above-specified small thickness), may be of any type of shape, and in particular they may be:

a) in the form of sheets (which may be said to be films if the sheets in question are of “great” length);

b) in the form of elements cut out from a sheet without cutting out a hole (a recess) passing through the thickness of said sheet (said elements consisting of pieces of sheets (strips or bars, for example) such as, or optionally worked over a portion of their thickness (a portion only of their thickness); or indeed

c) in the form of elements cut out from a sheet with through hole(s) (recesse(s)) cut out in the thickness of said sheet (which elements may present any shape).

The cutting in question is conventional cutting, performed using conventional mechanical means (advantageously cutting by waterjet(s), with two parallel blades, or with a cutter die).

Thus, the composite pyrotechnic products of the invention may consist in particular:

a) in an explosive sheet (usable as demolition material, as cutting material, as metal-forming material, (see point a) above);

b) in an explosive bar with a V-groove (usable as an element forming part of a detonating cutter cord, said V-groove being aimed to be covered with a metal coating or with a coating loaded with metal particles) (see point b) above); or

c) in a miniaturized array for multipoint initiation of explosive charges (see point c) above).

This last type of product of the invention is particularly preferred. The channels of the miniaturized array naturally present a section that is at least equal to the critical detonation dimension of the composition in question. They may present changes of direction with large angles, up to 90° (given the small values of said critical dimensions). They are generally square or rectangular in section.

Such arrays of the invention are particularly advantageous. Their shapeability (inherent to the nature of the binder present in their composition and to their small thickness) enable them to be used both on surfaces that are plane (it is possible to initiate a charge of cylindrical shape in conventional manner using such an array positioned on one of the bases of the charge) and on surfaces that are curved (such unconventional positioning can be particularly advantageous for increasing the speed of shrapnel in one direction).

In a second aspect, the invention provides a method of preparing (obtaining) composite pyrotechnic products of the invention, as described above. In characteristic manner, said method is based on using at least one cylinder mill (or roller mill). In characteristic manner, it comprises incorporating charges in the binder in a cylinder mill. More precisely, it comprises:

-   -   incorporating charges in the gum raised to a temperature of at         least 50° C., generally to a temperature in the range 60° C. to         80° C.; said incorporation being performed in a cylinder mill;         and     -   calendaring the resulting loaded sheet, in a cylinder mill.

Any plasticizer or additive involved is also incorporated in the gum in the cylinder mill.

A cylinder mill (or roller mill) is a device that is itself known.

Using such a mill makes it possible to obtain products of the invention (it makes it possible to incorporate large contents of small charges in the gum), it enables the products to be obtained in highly advantageous manner (without making use of a solvent (which is very advantageous compared with certain prior art methods), at temperatures that are compatible with the sensitivity of the charges, with mixing and rolling being performed in a single step, in a single station (which is very advantageous compared with certain prior art methods)).

It may be considered that the present invention relies on selecting the binder in association with selecting the method, this double selection making it possible not only to obtain products of the invention (products loaded with a large content of fine sensitive charges) (where the feasibility of said method was not clear in advance), but to do so under working conditions that are simple.

The mixture is made up in the cylinder mill in conventional manner, with the cylinders rotating in opposite directions at different speeds.

When the gum is present in the form of granules, it is initially worked coarsely in a roll mill in order to obtain a thin strip (thickness 1 mm to a few millimeters).

Said gum is generally initially introduced into the cylinder mill while its cylinders are raised to a temperature (T) of at least 50° C. (less than 120° C., generally less than 100° C.), advantageously in the range 60° C. to 80° C. (60° C.≤T≤80° C.), e.g. 70° C. Thereafter, the charges and any other ingredient(s) (optional plasticizer(s) and additive(s)) are introduced, either separately or in a mixture. As a general rule, a charges+ingredient(s) mixture is prepared beforehand when such at least one ingredient is involved, and it is the mixture that is introduced into the mill. Charges may advantageously be introduced in a plurality of sequences after adjusting the spacing of the cylinders. The coating that builds up around the faster-turning cylinder can be recovered (cut away with a cutter), folded, and reintroduced between the cylinders (in order to make the distribution of the charges more uniform), in the usual manner for this method.

This produces a sheet (a film) of small thickness (corresponding to the spacing between the rollers). In order to adjust said thickness to the desired value (0.4 mm≤e≤5 mm, advantageously 1 mm≤e≤2 mm, most advantageously e≤1.5 mm), or indeed merely for eliminating thickness irregularities (it is desired for the thickness to be constant, uniform, and well-controlled), said sheet is calendared in a cylinder mill (the cylinders of said cylinder mill then rotate in the same direction, at the same speed, with the spacing between them being adjusted to the desired thickness value, or to a smaller value since there are two phenomena that might occur: the material might force the cylinders apart, and the products might relax after being rolled).

It can be understood that the successive steps of the method of the invention—obtaining the mixture in the form of a product of small thickness (sheet) and calendaring—are performed most advantageously with the same cylinder mill. Thus, at a single station, mixing, rolling, and calendaring are all performed; thus, at a single station, it is possible to obtain a sheet type product of the invention directly (the desired product or the product suitable for use in preparing other desired products of the invention, in particular by being cut).

The method of the invention may thus further include cutting the calendared and loaded sheet, advantageously by waterjet(s), using two parallel blades, or a cutter die.

Cut-out elements are thus obtained as specified above. Said cut-out elements can also be worked, as mentioned above.

The cutting of the sheets, more particularly when using blades, can be facilitated by heating said sheets beforehand to a temperature in the range 40° C. to 50° C.

I. The invention is illustrated below in non-limiting manner in its product and method aspects, by the following examples.

1. Raw Materials Used A) Gums

Urepan® 643 G: sold by the supplier RheinChemie (product of polyaddition of diphenyl-methane diisocyanate and a polyester). It presents the following characteristics:

-   -   number average molecular weight: 80,000 g/mol;     -   Mooney viscosity: 40 (±10) ML (5+4) at 100° C.

Urepan® 600: sold by the supplier RheinChemie (product of polyaddition of toluene diisocyanate and a polyester). It presents the following characteristics:

-   -   number average molecular weight: 40,000 g/mol;     -   Mooney viscosity: 26 (±6) ML (5+4) at 100° C.

B) Charges

Hexogen (RDX) is as sold by the supplier Eurenco under the reference RDX M3c (D₁₀=1 μm, D₅₀=4 μm, and D₉₀=9 μm).

Hexanitrohexaazaisowurtzitane (CL20) is prepared and finely ground prior to use. Its grain size cut is characterized as follows: D₁₀=0.5 μm, D₅₀=4.7 μm, and D₉₀=12.2 μm.

2. Method of Preparing Composite Pyrotechnic Products of the Invention

Composite pyrotechnic products of the invention have been prepared and tested as follows.

Their composition by weight and their (measured) critical detonation diameter are given respectively in the table below.

These composite pyrotechnic products of the invention have been obtained from the above-identified raw materials.

Step a) of the method: pasty mixtures were obtained using a cylinder mill, in known manner. In order to obtain each of said mixtures, the gum in question was initially introduced between the rollers and raised to a temperature of 70° C. That softened it. Thereafter, a mixture of charges plus plasticizer, previously prepared in a container, was added. In Example 8, only the charges were added. Once all of the charges were incorporated in the gum, the milling was continued for about 15 minutes (min). At this stage (see Example 1), it was possible to incorporate small quantities (0.3% in said Example 1) of candellila wax very progressively in order to lubricate the loaded gum and the cylinders. After incorporating the wax, milling was continued for five minutes. By then, one of the cylinders was coated. Finally, rotation of the cylinders was stopped and the coating was cut width-wise in order to be recovered in the form of a sheet (dimensions: 250 mm×150 mm). Depending on the spacing of the cylinders, the resulting sheets presented a “single” thickness of about 2 mm, 1.5 mm, or 1 mm.

Step b) of the method: calendaring was performed to adjust and/or make more uniform the thickness of the sheets that were obtained. Said sheets were passed between the two cylinders of the same cylinder mill, set at the desired spacing, and rotating in the same direction, at the same speed. This time, the sheets did not wind around a cylinder. Calendaring was performed. Once the calendaring stage was terminated, the product obtained in the form of a sheet was uniform and presented constant thickness (of 2 mm, 1.5 mm, or 1 mm).

Step c) of the method: the sheet was cut into channels of various sections using specific tooling, made up essentially of two parallel blades of spacing guaranteed by washers of calibrated thicknesses. The sheets were cut up after being raised to a temperature of 45° C.

3. Results

Ingredients (% by weight) Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 Urepan ® 643G 9.4 9.39 8.8 8.2 — 11.2 10.4 — Urepan ® 600 — — — — 9.39 11.7 TEGDN 2.3 2.35 2.9 3.5 2.35 2.8 2.6 — RDX 88 88.26 88.3 88.3 88.26 88.3 CL20 86 87 Critical detonation section (+: detonation; −: no detonation) 2 · 2 mm² + + + + + + + + 1.5 · 1.5 mm² + + + + + − + − 1 · 1 mm² + + + − − − −

The compositions of Examples 1, 2, and 3 containing RDX charges are particularly advantageous in that they present a critical detonation section that is less than or equal to 1 mm².

The compositions of Examples 6 and 7, containing CL20 charges present critical detonation sections that are larger (the critical detonation section of the composition of Example 6 is greater than 1.5 mm² and the critical detonation section of the composition of Example 7 lies in the range 1 mm² to 1.5 mm²) than the critical detonation sections of Examples 1, 2, and 3 containing RDX charges. The increase in the charge content leads logically to a decrease in the critical detonation section (the charge content of the composition of Example 6 is 86% whereas the charge content of the composition of Example 7 is 87%).

II. The advantage of the present invention can clearly be seen from a consideration of the following observations.

a) Binder=hydroxyl-terminated polybutadiene (HTPB) (sold by the supplier Cray Valley under the name R45HT) of number average molecular weight 2800 g/mol (binder conventionally used in the context of composite energetic products).

a1) (Very viscous) pastes were obtained by milling using said binder (20% by weight) and RDX charges (80% by weight), referenced M3c from Eurenco, presenting a grain size distribution with a D₁₀ value of 1 μm, a D₅₀ value of 4 μm, and a D₉₀ value of 9 μm (see above). They were cast, with difficulty, (at small thickness) in molds made of polymethyl methacrylate (PMMA) (stepped test pieces) and they were tested within said molds (any unmolding would involve degradations) in order to evaluate their critical sections. The critical sections were about 3 mm².

a2) (Very viscous) pastes of the same type containing, in addition to the HTPB and the charges, an effective quantity of a curing agent (diisocyanate), were prepared by miffing. They were cast in molds in order to be in the form of sheets of small thicknesses. Said sheets were heat treated to cure the HTPB (via its hydroxyl-terminated functions). The shrinkage that occurs during curing meant that it was not possible to control the thickness of the cured sheets. Specifically, in order to obtain sheets of controlled small thickness (e.g. 2 mm), it was necessary to proceed as follows: obtain sheets of substantial thickness (e.g. 10 mm) by molding, subject them to heat treatment, and then machine them to said controlled small thickness.

a3) It was not possible by milling to obtain pastes with said binder containing more than 80% by weight of small RDX charges (D₁₀=1 μm, D₅₀=4 μm, and D₉₀=9 mm: referenced M3c from Eurenco (see above)).

a4) An RDX charge content of 85% by weight in said binder (15% by weight) could be obtained only by using a plurality of grain sizes for RDX charges: 65% of the weight of RDX, referenced M3c from Eurenco (see above) and 20% by weight of RDX having a larger grain size (D₅₀=35 μm). Nevertheless, the resulting pastes could not be rolled between the rollers given their sticky nature. They were cast (in very small thicknesses) in PMMA molds (stepped test pieces) and tested within said molds (any unmolding involving degradation) to evaluate their critical section. Given the presence of large RDX charges, their critical section was greater than 5 mm².

b) Binder=lauryl methacrylate.

This binder, which is very liquid, made it possible to incorporate a high content of small charges therein. It must nevertheless necessarily be cured. Pastes containing 14% by weight of lauryl methacrylate (+curing agent: diisocyanate) and 86% by weight of CL20 (of grain size distribution presenting a D₁₀ value of 0.5 μm, a D₅₀ value of 4.7 μm, and a D₉₀ value of 12.2 μm (see above)) were prepared. They were cast in molds in order to be in the form of sheets of small thicknesses. Said sheets were subjected to heat treatment to cure the lauryl methacrylate. The shrinkage that occurred during curing meant that it was not possible to control the thickness of the cured sheets. Specifically, in order to obtain sheets of controlled small thickness (e.g. 2 mm), it was initially necessary to proceed as follows: obtain sheets of substantial thickness (e.g. 10 mm) by molding, subject them to heat treatment, and then machine them to said controlled small thickness. 

1. A composite explosive product, wherein: its composition expressed as percentages by weight comprises: +85% to 92% of organic energetic charges; said organic energetic charges a) being selected from charges of octogen (HMX), hexogen (RDX), hexanitrohexaazaisowurtzitane (CL20), penthrite (PETN), and mixtures thereof, and b) presenting a grain size distribution with a value for D₉₀ less than 15 μm and a value for D₅₀ less than or equal to 5 μm; and +7% to 12% of a polymer gum selected from polyurethane-polyester gums, polyurethane-polyether gums, and mixtures thereof, of number average molecular weight greater than 20,000 g/mol and of Mooney viscosity lying in the range 20 to 70 ML (5+4) at 100° C.; and wherein the composite explosive product presents a thickness lying in the range 0.4 mm to 5 mm.
 2. The composite explosive product according to claim 1, wherein said energetic charges are selected from charges of hexogen (RDX), of hexanitrohexaazaisowurtzitane (CL20), and mixtures thereof,
 3. The composite explosive product according to claim 1, wherein said polymer gum is a polyurethane-polyester gum or a polyurethane-polyether gum.
 4. The composite explosive product according to claim 1, wherein said polymer gum presents a number average molecular weight greater than 35,000 g/mol.
 5. The composite explosive product according to claim 1, wherein its composition further includes at least one plasticizer, selected from energetic plasticizers, non-energetic plasticizers, and mixtures thereof; said at least one plasticizer generally being present at a content of 1% to 4% by weight.
 6. The composite explosive product according to claim 1, wherein its composition further includes at least one additive; said at least one additive generally being present at a content of 0.1% to 1% by weight.
 7. The composite explosive product according to claim 1, wherein the composite explosive product is in the form of a sheet or of an element cut out from a sheet without cutting out holes passing through the thickness of said sheet, or in the form of an element cut out from a sheet with through hole(s) being cut out in the thickness of said sheet.
 8. The composite explosive product according to claim 7, wherein the composite explosive product consists in an explosive sheet, an explosive bar with a V-groove, or in a miniaturized array for multipoint initiation of explosive charges.
 9. The composite explosive product according to claim 1, wherein the composite explosive product it consists in a miniaturized array for multipoint initiation of explosive charges suitable for use on a plane surface or on a curved surface of said explosive charges.
 10. A method for obtaining a composite explosive product according to claim 1, the method comprising: incorporating said charges in said gum raised to a temperature of at least 50° C.; said incorporating being performed in a cylinder mill; and calendaring the resulting loaded sheet in a cylinder mill.
 11. The method according to claim 10, the method further comprising: cutting up the calendared loaded sheet.
 12. The composite explosive product according to claim 1, wherein its composition comprises 88% to 90% of organic energetic charges.
 13. The composite explosive product according to claim 1, wherein its composition comprises 8% to 10% of the polymer gum.
 14. The composite explosive product according to claim 1, wherein the composite explosive product presents a thickness lying in in the range 1 mm to 2 mm.
 15. The composite explosive product according to claim 3, wherein said polymer gum is a polyurethane-polyester gum.
 16. The composite explosive product according to claim 4, wherein said polymer gum presents a number average molecular weight greater than 75,000 g/mol.
 17. The composite explosive product according to claim 5, wherein said at least one plasticizer is present at a content of 2% by 3% by weight.
 18. The method according to claim 10, wherein the temperature is in the range 60° C. to 80° C.
 19. The method according to claim 11, wherein the cutting up is performed with waterjet(s), with two parallel blades, or with a cutter die. 